Celtic - Ogham Stones - from left to right - February ( Willow ) Earth ( Beech, the Phagos ) and Water ( Poplar ). Hanging near the socle of the Southern Cross at Monasterboice, Ireland - The ogham alphabet is said to have originated in the fourth or fifth century in southern Ireland. It is widely regarded as the oldest alphabet used in Ireland. The alphabet takes its name from Ogma the ancient Celtic god of elocution or fine speech. It was Ogma, as legend has it, who inspired this alphabet. The main twenty letters in this alphabet are divided into four categories of five sounds (see Alphabet). These twenty letters share their names with twenty trees that are known to have been sacred to the Druids. The Druid people were probably the primary users of this alphabet. The 15th century Book of Ballymote confirms that Ogham was a secret language used in many Druid rituals.